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City sics beetles on river tamarisk

Tamarisk along the northern bank of the Colorado River has a new neighbor: 8,000 tamarisk beetles that feed solely on the water-sucking plant.

The city of Grand Junction removed tamarisk and fostered four acres of wetland more than a year ago along the river near Riverside and Redlands parkways. The new wetland area was created after seven-tenths of an acre of wetland was eliminated along Patterson Road between 24 1/2 and 25 1/2 roads during the Ranchmen’s Ditch project. The project involved installing pipes that would guide rain water from storms on the Bookcliffs to the Colorado River without causing flooding along the way.

Within months, the tamarisk in the new wetland area was back. The city considered spraying a herbicide to kill the new growth, City Project Engineer Dave Donohue said.

“We concluded if we did that, we’d have so much herbicide on new wetlands plants and water, it would be a disaster,” Donohue said.

So, Donohue pursued a different tamarisk-killer: the tamarisk beetle. Palisade Insectary Director Dan Bean released 7,000 tamarisk beetles at the site two weeks ago and another 1,000 Wednesday. Eggs and larvae already are appearing this week, showing the beetles are spreading into their new habitat and leaving offspring behind. The beetles regulate their numbers based on available food, Bean said, so he doesn’t expect them to overpopulate the area. Bean said the beetles aren’t likely to enter homes, and they don’t eat anything but tamarisk.

The insectary is one of a few in the country and the only one in Colorado, Bean said. It’s run by the Colorado Department of Agriculture and was placed in Palisade in the 1940s to provide predatory wasps to eat oriental fruit moths, which were destroying peach crops. The insectary continues to collect insects from inside and sometimes outside the state to help farmers, ranchers and gardeners fight pests across Colorado. The tamarisk beetles released along the Colorado River were collected in De Beque Canyon.

Bean said the beetles’ effect may not be instant, but they eventually could help kill tamarisk plants for miles along the river.

“It takes several defoliations to help them die back, but the beetles will come back and hit an area again and again,” he said.

The city isn’t the first government body to enlist the insectary’s help. The insectary worked with the U.S. Bureau of Land Management to release tamarisk beetles in Horse Thief Canyon.